1. Field of the Invention
The present invention relates to a sheet processing apparatus that corrects lateral deviation of a sheet that has been conveyed and carries out post processing such as punching and sorting on the corrected sheet.
2. Description of the Related Art
Conventionally, there has been known a technique to correct lateral deviation of a sheet, which has been conveyed from an image forming apparatus, in a width direction perpendicular to a conveying direction in a sheet processing apparatus.
Examples of such a sheet processing apparatus include one which corrects lateral deviation of a sheet in the width direction by detecting a side edge of the sheet, moving the sheet in the width direction, and aligning the side edge of the sheet with a predetermined position (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2007-001761). In this conventional sheet processing apparatus, processing such as punching and sorting is carried out on a sheet whose lateral deviation has been corrected.
In the conventional sheet processing apparatus described above, however, a shift unit configured such that guide members and rollers for sheet conveyance move thereon so as to correct for lateral deviation of a sheet in the width direction is used, and hence the shift unit itself is heavy in weight. Moreover, a motor, which is a drive source, and the shift unit are connected together by a belt, and hence there may be cases where operation of the motor and movement of the shift unit are not started in synchronization with each other under the effect of an inertial force due to the weight of the shift unit and the expanding and contracting properties of the belt. In such cases, the travel amount of the shift unit is calculated based on information on a drive signal for the motor, and when based on the calculated amount, it is determined that the shift unit has reached a predetermined position, and the shift unit is stopped, a position at which the shift unit is desired to be stopped and a position at which the shift unit has actually stopped do not match.
Moreover, the amount of delay in the shift unit actually starting operating with respect to a time when the motor starts operating is also dependent on the expanding and contracting properties of the belt, and hence this amount of delay varies according to the distance from a motor shaft to a place at which the belt and the shift unit are fixed. Thus, when the position at which the shift unit stops varies each time the shift unit operates, the amount of delay cannot be uniform.